Preparation of phosphine oxide compounds



United States Patent 3,082,256 EREEARATEON (ll PHGSI'HlNE (BXIIDEQGMPGUNDS Harold'i ames liarwood and Kenneth A. Poli'art, Dayton, (Shin,assigncrs to Monsanto Qhernical Qornpany, St. Louis, Mo., a corporationoi Delaware No Drawing. Filed .iuiy 20, 1959, Ser. No. 828,042 3 Ciainr(Cl. Mo -696.5)

The present invention relates to the preparation of organic compounds ofphosphorus and more particularly provides a new and valuable method ofpreparing phosphine oxide compounds of the formula i R--P-R in which Ris a hydrocarbyl radical free of aliphatic unsaturation and containingfrom 1 to 8 carbon atoms and R and R" are selected from the classconsisting of R and chlorine.

We have found that compounds of the above formula are readily preparedby treating the corresponding phosphorus-sulfur compounds with thionylchloride or bromide, the reaction occurring substantially according tothe scheme s ll It wherein R, R and R are as herein defined and X ischlorine or bromine.

One class of phosphorus-sulfur compounds having the above formula anduseful for the present purpose includes the trihydrocarbylphosphinesulfides. Conversion thereof to the trihydrocarbylphosphine oxidesproceeds according to the following equation.

Z Z I Z! I Phenyl Phenyl Phenyl Ethyl Ethyl Methyl Methyl Methyl PhcnylOyclchcxyl Oyclohexyl CYClOllEJXYl Benzyl Benzyl Bcnzyl 4-t0lyl 4-tolyl4-tolyl 2-ethylhexyl 2-6 thylhexyl Methyl Benzyl Ethyl Ethyll-isopropylphenyl Butyl Butyl Oetyl Phenyl Phenyl 2-cthylbenzyl2-ethylbenzyl Z-ethylbenzyl Oyclopropyl Cyclopropyl Oyclopropyl IsobutylOetyl Octyl Pentyl Pentyl Q-methylcyclopentyl Phenyl CyolohexylGyelohexyl Xylyl Xylyl Xylyl Methyl Ethyl Phenyl Hexyl Hexyl Ethyl Themixed trihydrocarbylphosphine sulfides which may be used to prepare thecorresponding trihydrocarbylphosphine oxides according to the inventionare readily obtained, e.g., according to the process of our copendingapplication Serial No. 828,044, filed July 20, 1959, whereindihydrocarbylphosphinothioic halides are reacted with ahydrocarbylmagnesiurn halide to give the trihydrocarbylphosphinesulfides.

Dihydrocarbylphosphinothioic chlorides are likewise converted, accordingto the invention, to give the corresponding oxygen compounds. Thus:

The dialkylphosphinothioic chlorides are thus converted.

to the dialkylphosphinic chlorides and the diarylphosphinothioicchlorides are converted to the. diarylphosphinic chlorides. Examples ofdihydrocarbylphosphinic chlorideprepared from the correspondingphosphinothioic chlorides according to the present process are shownbelow:

Ethyl Ethyl Methyl Methyl Isopropyl Isopropyl' 'utyl Butyl Pentyl Pentylexyl Hexyl Heptyl H'eptyl 2-ethylhexyl 2-ethylhcxyl Octyl Octyl MethylEthyl Isopropyl Butyl 2-ethylhexyl Ethyl Phony} Phenyl' Phenyl Methyl4-t0lyl i-tolyl 4-ethylphenyl A-ethylphcnyl Benzyl Benzyl Benzyl EthylOyclopeutyl Cyclopentyl Gyclohcxyl Cyclohexyl Phenyl Isopropyl BenzylPhenyl Cyclopropyl Oyclopropyl z-phcuylethyl Z-phenylothyl Ethyl4-ethylbenzyl Oyclohexyl Pentyl Methyl 2-methylcyclopentyl In prior art,the dihydrocarbylphosphinic halides have been obtainable onlywithdifficulty and in low yields. Thus, as reported by H. lean et al.,Bull. Soc. Chim. France (1956), 569-70, from. the mixture or" reactionproducts obtained from either methylmagnesium chloride orethylrnagnesium chloride there is obtained upon dry vacuum distillationonly a 10% yield of the dimethylphosphinic chloride or thediethylphosphinic chloride. The compounds RPOCl or R POCl (Where R ismethyl or ethyl) are said to remain strongly complexed with magnesiumand can only be partially separated by using ether as a solvent. Whenmethylmagnesium bromide was used instead of the corresponding chloride,the products contained bromine. i

As will beshown hereinafter, the present processgives thedihydrocarbylphosphinic .halidesin. very good yields. The startingvmaterials, i.e., the phosphinothioic halides, are readily obtained bychlorination of the tetrahydrocarbyl bi(phosphine sulfides) which, asreported by Reinhardt et' al., Chem. Berichte 90, 1656 (1957), arereadily prepared by the reaction of thiophosphoryl chloride ,with. ahydrocarbylmagnesium bromide.

The present invention also provides a method of preparinghydrocarbylphosphonic dichlorides from the corresponding phosphonothioicdichlorides, thus:

Reaction of thionyl chloride or bromide with methylphosphonothioicdichloride thus gives methylphosphonic dichloride,

Other hydrocarbylphosphonic dihalides prepared according to theinvention are ethyl-, propyl-, butyl-, isopropyl-, pentyl-, hexyl-,heptyl-, 2-ethy1hexyl-, octyl-, phenyl-, 2-, 3-, or 4-tolyl-, benzyl-,2-phenylethyl-, 2-, 3-, or 4-ethylphenyl-, cyclopropyl-, cyclopentyl-,cyclohexyl, and the xylylphosphonic dichlorides.

Reaction of the trihydrocarbylphosphine sulfides, the dihydrocarbylphosphinothioic chlorides or the hydrocarbyl phosphonothioic chlorideswith thionyl chloride or bromide to give the corresponding oxygencompounds takes place readily at ordinary, elevated, or reducedtemperatures, depending upon the nature of the individualphosphorus-sulfur compound and of the thionyl halide. Using the quitereactive trihydrocarbylphosphine sulfides, reaction usually occurswithout application of heat; in some instances an exothermic reactionoccurs. When employing such compounds it is preferred to operate byadding the thionyl halide to the sulfide gradually at ordinary ordecreased temperatures, for instance, at a temperature of from to 20 C.Heating at, for instance, from 50 to 125 C. and preferably at therefluxing temperature of the reaction mixture may be necessary whenworking with the less reactive phosphinothioic halides orphosphonothioic dihalides. It is generally advantageous to operate inthe presence of an inert liquid diluent or solvent, e.g., benzene,toluene, hexane, dichlorobenzene, etc. The phosphorus-sulfur compoundand the thionyl halide are advantageously employed in stoichiometricproportions, i.e., one mole of the sulfur compounds per mole of thethionyl halide. However, an excess of the thionyl halide may be used andis often recommended to assure complete participation in the reaction ofthe less readily available compound. Completion of the reaction can begenerally ascertained by noting cessation in change of color andviscosity of the reaction mixture. The products, i.e., the phosphineoxides, the phosphinic halides, or the phosphonic halides are easilyisolated from the reaction products by simply removing the diluent andany excess of reactants which may have been employed.

As is known in the art, trihydrocarbylphosphine oxides are readilyhalogenated to dihalotrihydrocarbylphosphoranes. In some instances,sulfur monochloride formed as by-product in the conversion of thesulfides to oxides or excess thionyl halide will react with the oxides,thus:

where Z, Z and Z" are hydrocarbyl radicals.

While extent of halogenation will depend upon the nature of theindividual phosphine oxide, and upon the reaction conditions employed,conversion of any or all of the oxide product into the dihalide isimmaterial for the present purpose, since the dihalide, is formed, isreadily converted to the phosphine oxide by mixing with water, thus:

Of course, if desired, the dihalotrihydrocarbylphosphorane can beisolated and used per se, e.g., as an intermediate for the preparationof dialkylphosphinous chlorides by pyrolysis.

4.- The invention is further illustrated by, but not limited to, thefollowing examples.

Example 1 Thionyl chloride (0.034 mole) was added to a stirred solutionof triphenylphosphine sulfide (0.034 mole) in ml. anhydrous benzene atroom temperature. A very mild reaction appeared to take place and aftera few minutes a small amount of heavy oil separated. The pale yellowliquid was decanted from the heavy oil, and the solvent and low boilingcomponents removed under water pump vacuum with a minimum amount ofheating. The yellow solid which remained washed with Warm Water toremove any acidic chloro compounds (titration of the wash water showedit to contain 0.003 mole of HCl). The solid was then recrystallized fromdilute alcohol, to give the triphenyl phosphine oxide, M.P. 158, mixedM.P. with authentic compound 157-8.

Example 2 A solution of 6.33 g. (0.372 mole) of dimethylphenylphosphinesulfide in 35 ml. of benzene was chilled in an ice-bath and 10 ml. ofthionyl chloride was slowly added, with shaking, to the cooled solution.The reaction appeared to be mildly exothermic. The phosphine oxide thusformed was almost immediately chlorinated by S CI formed or the excessSOCl present. The mixture of solvent and yellow crystals which separatedwas refiuxed for one hour. After allowing the reaction mixture to coolto room temperature, the solid which formed was filtered otf. Uponwashing the solid with benzene and vacuum drying, there was obtained7.37 g. (93.8% theory) of dichloro dimethylphenylphosphorane, Ml.173.9-176 C. (sinters at C.). It was completely soluble in chloroform,and recrystallization from this solvent gave large, colorless cubiccrystals. The dichlorodimethylphenylphosphorane was converted todimethylphosphine oxide by hydrolyzing with water, removing HCl with anin exchange resin and evaporating to dryness.

Example 3 To an ice-cooled flask containing a solution of 12.1 g. ofdimethylphosphinothioie chloride in 35 ml. of benzene there wasgradually added, with shaking, 15 ml. or thionyl chloride. The resultingsolution was refluxed for 1.5 hrs. and then distilled to give 9.2 g.(86.7% yield) of dimethylphosphinic chloride, 13.1. 115-118 C./52 mm.,which solidified upon attaining room temperature.

What we claim is:

1. The method which comprises reacting, in the pres ence of an inertdiluent, a trihydrocarbylphosphine sulfide wherein the hydrocarbylradical is free of aliphatic unsaturation and contains from 1 to 8carbon atoms, with thionyl chloride and removing from the resultingreaction products a trihydrocarbylphosphine oxide wherein thehydrocarbyl radical is as herein defined.

2. The method which comprises reacting triphenylphosphine sulfide, inthe presence of an inert diluent, with thionyl chloride and recoveringtriphenylphosphine oxide from the resulting reaction product.

3. The method which comprises reacting dimethylphenylphosphine sulfidewith thionyl chloride to obtain a reaction product comprisingdichlorodimethylphenylphosphorane and mixing said product with water toobtain dimethylphenylphosphine oxide.

References Cited in the file of this patent FOREIGN PATENTS 1,056,606Germany May 6, 1959 OTHER REFERENCES Ishikawa: S. Chem. Abstracts, vol.22 (1928), p. 1581. Van Wazer: Phosphorus and Its Compounds, pp. 307-8,vol. 1 (1958).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent; No. 3,082256 March 19, 1963 Harold James Harwood et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3, line 65, for "is' first occurrence read Signed and sealed this25th day of February 1964.

(SEAL) Attest: ERNEST SWIDER EDWIN L. REYNOLDS Attcsting Officer Ac tingCommissioner of Patents

1. THE METHOD WHICH COMPRISES REACTING, IN THE PRESENCE OF AN INERTDILUENT, A TRIHYDROCARBYLPHOSPHINE SULFIDE WHEREIN THE HYDROCARBYLRADICAL IS FREE OF ALIPHATIC UNSATURATION AND CONTAINS FROM 1 TO 8CARBON ATOMS, WITH THIONYL CHLORIDE AND REMOVING FROM THE RESULTINGREACTION PRODUCTS A TRIHYDROCARBYLPHOSPHINE OXIDE WHEREIN THEHYDROCARBYL RADICAL IS AS HEREIN DEFINED.